This configuration entry is related to an Experimental (Optional) feature called Refined Types. Before you start to configure this section, make sure to read the page specific for this feature (accessible here) and this page that explains how to enable Experimental Features.
API Version v2.0.0 - Introduced fieldTypes configuration option.
Change the type of a model field defined by the key of this key-value pair to the type defined by the value of this key-value pair. To configure refined types, add the following lines to your configuration object: